Preheat oven to 375℉ with rack in middle position.
Prepare 9x13 casserole dish with nonstick cooking spray or butter.
Wash and dice (peeled or unpeeled) potatoes into ½-¾" cubes and place them in a large pot. Cover with salted water and bring to a boil. Reduce heat somewhat and cook until potatoes are fairly tender. (Don't overcook. Better to parboil than have them mushy. They will continue to cook when baked in the oven.)
While potatoes are cooking, combine all dairy (except cheese) and seasonings in a medium bowl. Incorporate ingredients with a hand mixer until fully combined.
When potatoes are ready, drain them and gently place them back in the now empty pot. Carefully fold in the mixed ingredients from the previous step, 1½ cups of the cheese, and 1 cup of the bacon into the potatoes, and then pour this mixture into your prepared casserole dish.
Top your potatoes with the remaining cheese, bacon, and Panko crumbs in that order.
Bake for 25-30 minutes.
When casserole is bubbly, remove from the oven and let sit for about 5-10 minutes. Top with the green onions and serve.